1. Field of the Invention
The present invention relates to a rechargeable battery. More particularly, the present invention relates to a rechargeable battery having an electrode assembly that has an improved shape.
2. Description of the Related Art
Unlike a primary battery that cannot be recharged, a rechargeable battery can be repeatedly charged and discharged. Low-capacity rechargeable batteries are used for portable compact electronic apparatuses such as mobile phones, notebook computers, and camcorders, and high-capacity rechargeable batteries are widely used as a power source for driving a motor of a hybrid vehicle, etc.
The rechargeable battery includes an electrode assembly having a positive electrode plate and a negative electrode plate are disposed and a separator interposed therebetween. The battery also includes a cap assembly that closes and seals the case and is electrically connected to the electrode assembly. In the case of a prismatic rechargeable battery, an electrode assembly is wound in a jelly roll shape so as to include a flat portion and curved portions disposed at both sides of the flat portion, and the flat portion is positioned closely adjacent to an inner wall of the case.
In a charging/discharging process of the above rechargeable battery, volume of the electrode assembly varies. For example, in a lithium ion battery, a negative electrode active material of a negative electrode plate occludes lithium ions during a charging process so that the volume of the negative electrode active material expands, and emits the lithium ions during a discharging process so that the volume is reduced. As described, the electrode assembly repeats expansion and reduction whenever a charging/discharging cycle is repeated.
However, most cases, excluding a pouch-type case, are rigid bodies formed of metal so that the case cannot accommodate the volume expansion of the electrode assembly. Therefore, various methods including reducing capacity of the electrode assembly to match internal capacity of the case or changing a spiral-winding structure of the electrode assembly have been suggested to deal with the volume expansion of the electrode assembly.
However, charging/discharging capacity of the rechargeable battery is also reduced when the capacity of the electrode assembly is reduced so that performance of the rechargeable battery is deteriorated. In addition, when the spiral-winding structure of the electrode assembly is changed, the shape and a manufacturing process of the electrode assembly are complicated so that production efficiency of the rechargeable battery is deteriorated.